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Human Genetics

Human Genetics. Some Important terms : 1. Dominant (tall peas) 2. Recessive (short peas) 3. Homozygous dominant TT recessive tt 4. Heterozygous Tt 5. Gene 6. Allele 7. Homologous Chromosomes 8. Linkage (many genes on the same chromosome)

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Human Genetics

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  1. Human Genetics Some Important terms: 1. Dominant (tall peas) 2. Recessive (short peas) 3. Homozygous dominant TT recessive tt 4. Heterozygous Tt 5. Gene 6. Allele 7. Homologous Chromosomes 8. Linkage (many genes on the same chromosome) 9. Crossing over (exchanges within chromosomes) 10. Phenotype What we express (Tall Pea) 11. Genotype What’s in our DNA (Tt)

  2. To determine the nature of inherited human diseases, it is often necessary to examine several generations of a human family. This record is called a Pedigree: Males are Females are Squares Circles

  3. A line represents a “union”, or an offspring So, here we have a man and a woman who have had 4 children, 3 boys and a girl.

  4. A filled square or circle means the person has the trait. So, here we have a man and a woman who have had 4 children, 3 males and a female. Two of the male offspring show the trait, but the female does not.

  5. A line represents a “union”, or an offspring A filled square or circle means the person has the trait. How could we explain this pattern of inheritance?

  6. Only individuals who are Homozygous for the recessive allele will show the trait: Cc Cc cc Cc Cc cc Tongue curling: C= Curled c= flat c= recessive allele cc= homozygous recessive

  7. What could cause this pattern of inheritance?

  8. What could cause this pattern of inheritance? THE PARENTS MAY BE HETEROZYGOUS (Cc Cc)

  9. What could cause this pattern of inheritance? Sex Linkage

  10. Text Fig. 7.19 Human Karyotype

  11. Males have only 1 X-chromosome, And a smaller y-chromosome Females Have 2 X-chromosomes Therefore, genes that are carried on the X-chromosome have 2 alleles in females, But only 1 allele in males

  12. Let’s consider an example: Color Blindness Caused by a recessive allele c. C =Normal vision C c c Males have only 1 X-chromosome, And a smaller y-chromosome Females Have 2 X-chromosomes A female can have one copy of the c allele and still not show the recessive trait---because her Dominant allele masks the effect A single copy of the recessive allele in a male results in the trait.

  13. Sex Linkage XCXc XCY Genotypes????

  14. Sex Linkage XCXc XCY XcY XcY XcY XcXc orXcXc Genotypes????

  15. Sex Linkage XCY XCXc

  16. Sex Linkage XCY XCXc XC XcXc ? XcY ? ? ? ? ?

  17. Text Fig. 7.24 Pedigree Royal Family Hemophilia

  18. POPULATION GENETICS CHANGE IN THE FREQUENCY OF ALLELES IN A POPULATION OVER TIME LET’S START WITH A POPULATION THAT CONTAINS AN EQUAL NUMBER OF HOMOZYGOUS NORMAL AND HOMOZYGOUS RECESSIVE INDIVIDUALS PARENTS AA x aa

  19. PAA x aa (2/4) A=50% (2/4) a=50% F1 Aa (1/2) A=50% (1/2) a=50% F1 x F1 F2 AA Aa aA aa (4/8) A=50% (4/8) a=50% The frequency of the two alleles DID NOT CHANGE OVER 3 GENERATIONS!

  20. POPULATION GENETICS THE HARDY-WEINBERG RULE (SEE TEXT 10.6--- PAGE 242) Godfrey Hardy was an English mathematician, and Wilhelm Weinberg was a physician. In 1908 they independently arrived at the same theory concerning the frequency of the alleles in a population.

  21. POPULATION GENETICS We can describe a population as being a “pool” of alleles….the gene “pool” of a species. We could, for example, examine the frequency of the alleles that regulate human tongue curling (in this room): C is the allele for curled tongues c is the allele for flat tongues if we let p=the frequency of the allele “C” and we let q= the frequency of the allele “c” then p + q = 1 ( fC+ fc = 100%) What would be your guess about the frequencies of C and c? in this room???

  22. POPULATION GENETICS Hardy and Weinberg were interested in the changes that might occur in the frequencies of the alleles in a population as a result of meiosis and sexual reproduction: What will the distribution of alleles be in a population if we look at it over several generations?

  23. PAA x aa (2/4) A=50% (2/4) a=50% F1 Aa (1/2) A=50% (1/2) a=50% F1 x F1 F2 AA Aa aA aa (4/8) A=50% (4/8) a=50% The frequency of the two alleles DID NOT CHANGE OVER 3 GENERATIONS! The frequency of the two alleles DID NOT CHANGE OVER 3 GENERATIONS! And it NEVER WILL CHANGE...True ????

  24. POPULATION GENETICS The hardy-Weinberg Equilibrium is true, if certain requirements are met by the population: 1. Mating must be random. 2. There can be NO mutations. 3. All the individuals must have equal viability and vigor. 4. There can be no migration into or out of the population.

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